Electric lamps generally comprise either an incandescent ohmic filament bulb and suitable fittings or a discharge bulb usually with electrodes for exciting the discharge. The resultant radiation is not always visible, in which case, the bulb is lined with phosphorescent material to provide visible light. It is known also to provide a bulb without electrodes and to excite it by applying external radiation, in particular microwave energy.
An electrodeless lamp using a microwave source is described in U.S. Pat. No. 6,737,809, in the name of FM Espiau et al., the abstract of which is as follows:
A dielectric waveguide integrated plasma lamp with a body consisting essentially of at least one dielectric material having a dielectric constant greater than approximately 2, and having a shape and dimensions such that the body resonates in at least one resonant mode when microwave energy of an appropriate frequency is coupled into the body. A bulb positioned in a cavity within the body contains a gas-fill which when receiving energy from the resonating body forms a light-emitting plasma.
Despite reference to a “bulb”, this specification does not describe a discrete bulb, separable from the lamp body.
In our earlier International Patent Application, published under No WO 02/47102, we described:
A lamp has a body of sintered alumina ceramic material and an artificial sapphire window. The body is initially moulded in green state and the window is pressed into a front recess. The combination is fired at a temperature of the order of 1500° C., to fuse the body into a coherent pressure-tight state with the window. After partial cooling to the order of 600° C., a pellet of excitable material is added through a rear, charging aperture. A disc of ceramic with frit is placed over the aperture. The disc is irradiated by laser to fuse the frit and the disc to the body, thus sealing the excitable material into the lamp.